Biomarker responses in eelpouts from four coastal areas in Sweden, Denmark and Germany

• Data suggested inhibition of CYP1A/EROD in selected polluted sites.
• AChE activity followed a season and region-specific pattern.
• AChE activity could be linked to pollution pressure in the selected sites.
• Differences between sites for GSI, CF and EROD levels were independent of seasons.
• Hierarchical clustering of biomarkers showed links on site and individual level.

To increase our understanding of possible chemical impacts on coastal fish populations in the Baltic Sea, Kattegat and Skagerrak, the viviparous eelpout (Zoarces viviparus) was used as sentinel species in two major sampling campaigns (spring and autumn) in 16 different coastal sites. Condition factor (CF), liver somatic index (LSI), gonad somatic index (GSI) were measured and the activity of the hepatic enzymes ethoxyresorufin-O-deethylase (EROD), glutathione reductase GR), glutathione S-transferase (GST), catalase (CAT) and muscular activity of acetylcholinesterase (AChE) were assessed. PAH metabolites in bile were also analyzed. The most notable finding in the data set was the low EROD activity in eelpouts collected at the relatively polluted region in Germany compared to the other regions, which could be due to an inhibition of the CYP1A-system or to adaptation to chronic exposure of pollutants in this area. Additionally, low AChE activity was noted in the German region in the autumn campaign and low AChE activity detected in the Danish region in the spring campaign. These differences suggest possible season-specific differences in the use and release of AChE-inhibiting chemicals in the Danish and German regions. Clustering of biomarkers on site level indicated a relationship between CF and GSI and suggested that sites with a high CF contained eelpout that put a larger effort into their larvae development. Clustering of the oxidative stress markers GR, GST and CAT on the individual level reflected a possible coordinated regulation of these enzymes. Overall, the results support the importance of taking into account general regional differences and seasonal variation in biomarker activity when monitoring and assessing the effects of pollution. Despite the expected seasonal variation for most of the measured endpoint, several markers (GSI, EROD and CF) vary similarly between all selected sites in both spring and autumn. This suggests that the differences between sites for these endpoints are independent of season.